1. Field of the Invention
The present invention relates to a method for displaying an image signal that is suited for such matrix type display devices in which pixels are arranged into a matrix form in lines and columns. The present invention further relates to a display device for magnifying and projecting onto a screen, an image that has been displayed on a small-size liquid crystal display device, to a display device to be used as a monitor for a video camera, and to a display device to be used as a light valve of the aforementioned various display devices.
2. Description of the Prior Art
LCDs (Liquid Crystal Displays) have been aggressively researched and developed because of their many features such as being light weight and having a small thickness. However, they have a few drawbacks including a difficulty in increasing their size into large screens. Therefore, in recent years, much attention has been rapidly and increasingly focused on projection type display devices which magnify and project an image displayed by a small LCD by means of a projection lens or the like to obtain a large-screen display image. A display device for magnifying and projecting onto a screen an image that has been displayed on a small-size liquid crystal display device (hereinafter, referred to as projection type display device) commercially available at present uses a twist nematic (hereinafter, referred to as TN) LCD that takes advantage of the rotary polarization characteristic of liquid crystals.
Active-matrix type LCDs have been advanced to higher densities and increased numbers of pixels so that they are utilized as data display use displays for personal computers and workstations, and also as audio-visual displays of the standard system (NTSC) and HDTV system. Further, as the active-matrix type LCD has been increased in the number of pixels, a demand has also grown for higher speeds of the operating clock of source drive (data line drive) ICs. As a result, source drive ICs of high-speed operating clocks are under development, while proposed are methods in which a plurality of source drive ICs are operated in parallel and source lines of plurally divided screen areas are driven at the same time.
Twisted nematic liquid crystal devices are known as one of such display devices. Thin film transistors as active elements are driven by a source driver IC and a gate driver IC. If necessary, a plurality of source driver ICs are used. However, at joints of adjacent source driver ICs there occurs brightness differences due to variations in components for signal processing, resulting in deterioration of the image quality. In order to solve the above problem, a correction circuit may be added for correcting the brightness differences, or the source driver ICs have digital inputs. However, such measures would involve increases in cost, circuit scale, and mounting area around the LCD panel.
Recently, high temperature polysilicon techniques and low temperature polysilicon techniques have been developed, and by using such techniques, the gate driver IC and the source driver ICs can be formed at the same time as the TFTs. An LCD panel involves high cost and difficulties to have a large-area display area, and it is put into practical use as display devices to be used as an image pickup monitor for video cameras (hereinafter, referred to as viewfinder) and the like. A common feature of LCD panels fabricated by the high-temperature polysilicon technique and the low-temperature polysilicon technique is that the gate driver IC and the source driver ICs can be formed on the same substrate as well as the TFTs simultaneously. Therefore, there is no need of mounting the gate driver IC and the source driver IC on the LCD panel after the LCD panel is fabricated. It is also unnecessary to additionally fabricate the source driver IC or the like. Thus, the cost of the LCD panel can be reduced.
However, there still remains a problem of low upper-limit operating speed of the source driver circuit and the like formed directly on the LCD panel. The range of operating frequency in which the source driver circuit and the like operate stably is generally from 1 to 3 MHz. This requires a shift register and the like in the source driver circuit to be provided in a multi-stage arrangement. If the operating frequency of the shift register is 2 MHz while the LCD panel needs to be operated at 40 MHz, then a frequency division by 40/2=20 is required. This means that the shift register needs to be provided in 20 lines. The larger the number of shift registers, the larger the area occupied by the shift registers and the larger the number of defects that occur in the fabricating process. Therefore, this is not favorable.
As described above, LCD panels fabricated by the polysilicon technique, particularly by the low-temperature polysilicon technique, have an advantage of high feasibility of low prices, thus promising as display monitors for future personal computers and workstations. On the contrary, they are difficult to realize higher-speed driving (higher data rate or wider band). Therefore, it is desirable that wideband (high data rate) progressive scanning image signals of personal computers, workstations, and the like, can be displayed onto a display such as matrix type LCD panels which is poor at high-speed scanning, as mentioned above, but has advantages of simplicity and a low price, without causing any deterioration of image quality.
An object of the present invention is to provide a method for displaying image signals and a device therefor, which method and device can display wideband (high data rate) progressive scanning image signals onto a display which is poor at high-speed scanning, such as matrix type LCD panels, without causing any deterioration of image quality.
Another object of the present invention is to provide a projection type display apparatus or the like using the above-mentioned method and device.
In one aspect of the invention, first, odd-line signals are extracted from progressive scanning image signals in a first frame, and the extracted,signals are displayed onto odd lines in a display panel with a dot matrix. Subsequently, even-line signals are extracted from progressive scanning image signals in a second frame consecutive to the foregoing first frame, and the extracted signals are displayed onto even lines in the display panel. Thus, an image of one frame is displayed in the display panel in two frame periods. If one frame is provided each {fraction (1/60)} second, an image is displayed each {fraction (1/30)} second.
In a second aspect of the invention, first, odd-line signals are extracted from progressive scanning image signals in a first frame, and each of the extracted signals are displayed onto an odd line and an even, line adjacent to the odd line in the display panel at the same time. Thus, an odd-line signal is displayed along two adjacent lines. Subsequently, even-line signals are extracted from progressive scanning image signals in the second frame consecutive to the foregoing first frame, and each of the extracted signals are displayed onto an even line and an odd lines adjacent to the even line in the display panel at the same time. Thus, an odd-line signal is also displayed along two adjacent lines. Then, for example, first and second line signals are displayed in a second line in the display panel, and second and third line signals are displayed in a third line in the display panel. Thus, an image of one frame is displayed in the display panel in two frame periods.
In a third aspect of the invention, signals of odd-lines (2nxe2x88x921) are extracted from progressive scanning image signals in a first frame, and pixels in lines (4nxe2x88x923) of a display panel hold the image signals of a first polarity with, respect to a potential of a counter electrode in a display panel, while pixels in lines (4nxe2x88x921) hold the image signals of a second polarity, where xe2x80x9cnxe2x80x9d denotes an integer and the first polarity is positive polarity or negative polarity while the second polarity is a polarity opposite to the first polarity. Subsequently, signals of even-lines 2n are extracted from progressive scanning image signals in a second frame consecutive to the first frame, and pixels in lines (4nxe2x88x922) of the display panel hold the image signals of the first polarity, while pixels of lines 4n hold the image signals of the second polarity. Thus, an image of one frame is displayed in two frame periods. Further, in a third frame consecutive to the second frame, the pixels in-lines (4nxe2x88x923) and lines (4nxe2x88x921) of the display panel hold the image signals in such a way that the image signals have polarities opposite to those of the image signals held in the first frame. Subsequently, in a fourth frame consecutive to the third frame, pixels in lines (4nxe2x88x922) and lines 4n hold the image signals in such a way that the image signals have polarities opposite to those of the image signals held in the second frame. Then, for example, signals of 480 horizontal scan lines can be displayed in a display panel having 960 lines.
In a fourth aspect of the invention, wherein a period consists of four fields, image signals are extracted from interlace scanning image signals in a first field, and pixels of lines (4nxe2x88x923) and (4nxe2x88x922) in the display panel hold image signals of the first polarity, while pixels of lines (4nxe2x88x921) and (4n) hold image signals of the second polarity. Subsequently, image signals are extracted from interlace scanning image signals in a second field consecutive to the first field, and pixels of lines (4nxe2x88x922) and (4nxe2x88x921) hold image signals of the first polarity, while pixels of lines (4n) and (4n+1) hold image signals of the second polarity. Further, in a third field consecutive to the second field, the pixels of the display panel hold image signals in such a way that the image signals have polarities opposite to those of the image signals held in the first field. Subsequently, in a fourth field consecutive to the third field, the pixels hold image signals in such a way that the image signals have polarities opposite to those of the image signals held in the second field.
In a fifth aspect of the invention, it is assumed that if xe2x80x9cnxe2x80x9d denotes an integer, then a first polarity is positive polarity or negative polarity while a second polarity is a polarity opposite to the first polarity. First, image signals are extracted from progressive scanning image signals in a first frame, and pixels of lines (4nxe2x88x923) and (4nxe2x88x922) of the display panel hold first image signals of the first polarity, while pixels of lines (4nxe2x88x921) and (4n) hold second image signals of the second polarity. Subsequently, image signals are extracted from progressive scanning image signals in a second frame consecutive to the first frame, and pixels of lines (4nxe2x88x923) and (4nxe2x88x922) hold third image signals of the second polarity, while pixels of lines (4nxe2x88x921) and (4n) hold fourth image signals of the first polarity. By the above two frame periods, one-frame image information is displayed in the display panel.
In a sixth aspect of the present invention, it is assumed that if xe2x80x9cnxe2x80x9d denotes an integer, then a first polarity is positive polarity or negative polarity while a second polarity is a polarity opposite to the first polarity. First, image signals are extracted from interlace scanning image signals in a first field, and pixels of lines (8nxe2x88x927) and (8nxe2x88x926) on the display means hold first image signals of the first polarity, while pixels of lines (8nxe2x88x925) and (8nxe2x88x924) hold the first image signal of the second polarity, and pixels of (8nxe2x88x923) and (8nxe2x88x922) hold second image signals of the first polarity, while pixels of lines (8nxe2x88x921) and (8n) hold the second image signals of the second polarity. Subsequently, image signals are extracted from interlace scanning image signals in a second field consecutive to the first field, and pixels of lines (8nxe2x88x925) and (8nxe2x88x924) hold third image signals of the first polarity, while pixels of lines (8nxe2x88x923) and (8nxe2x88x922) hold the third image signals of the first polarity, and in which pixels of lines (8nxe2x88x921) and (8n) holds fourth image signals of the second polarity, while pixels of lines (8n+1) and (8n+2) hold the fourth image signals of the first polarity. Thus, an image of one frame is displayed in two field periods.
In a seventh aspect of the invention, a projection type display apparatus uses, as a light valve, a display device (display panel or the like) to which an image display device according to the present invention or an image signal display method according to the present invention is applied. Preferably the image display device or the display device is arranged each one for three optical paths of red (R), green (G), and blue (B). Among these three image display devices, the phase of a signal applied to an arbitrary line of one display device is opposite to the phase of a signal applied to the same line of another display device.
A display device according to a first aspect of the present invention comprises pixel electrodes arranged in a matrix form and a polarization plate placed on at least one of an incident surface or an outgoing surface of light. The display device further comprises, for the pixel electrodes, a drive means for applying a signal to the pixel electrodes in such a way that the pixel electrodes arranged in a matrix form are brought into either a first state that their polarities are different alternately in the unit of one line or a plurality of lines, or a second state that their polarities are different alternately in the unit of one column or a plurality of columns.
The polarization axis of the polarizing plate is so oriented as to be generally coincident with the direction of the columns for the first state, or with the direction of the lines for the second state. Also, when no polarizing plate is used, the signal lines are coated with a low dielectric film or a resin light-shielding film.
The display device according to a second aspect of the present invention comprises a color filter corresponding to the pixel electrodes, and a dielectric thin film formed on the opposite electrode or the pixel electrode in correspondence to the colors of the color filters. The dielectric thin film absorbs light of the ultraviolet region. The absorbency of each dielectric thin film for ultraviolet rays is varied by varying the thickness of the dielectric thin films depending on the color of the color filters. When a color filter is blue, the dielectric thin film is relatively thin, and when a color filter is red, the dielectric thin film is relatively thick. As a result of this, in manufacturing processes of the display device, the differences in film thickness among the dielectric thin films allow the quantity of ultraviolet rays incident on the liquid crystal layer to be varied, so that liquid crystal droplets can be provided in such sizes as to correspond to the individual color filters and offer an optimum scattering characteristic.
A display device according to a third aspect of the present invention comprises transparent electrodes arranged in a matrix form, and light-absorbing films of black or the like formed at a lower layer under the transparent electrodes. When the liquid crystal layer is in a transparent state, the light-absorbing films are recognized via the liquid crystal layer and the transparent electrodes (black display). When the liquid crystal layer is in a scattering state, only the scattering state of the liquid crystal layer is recognized (white display). Preferably, switching devices such as TFTs are formed under the transparent electrodes. The light-absorbing films are patterned opposite to the pixel configuration, and the TFTs have insulating films formed thereon.
An advantage of the image display method of the present invention is that progressive scanning image signals can be displayed at a half of a speed of the as-received signals.
Another advantage of the image display method of the present invention is that interlace scanning image signals can be displayed at a half of a speed of the as-received signals.
A further advantage of the image display method of the present invention is that a structure of a driving circuit can be simplified.
A different advantage of the image display method of the present invention is that image signals can be displayed in a display device having a larger number of horizontal scan lines than that of the signals.
An advantage of a liquid crystal display of the present invention is that light leakage near pixel electrodes due to a lateral electric field can be prevented.